A study released by Dr. James Hansen, the dean of climate scientists and director of the Nasa Goddard Institute for Space Studies, concludes that the recent heat waves and extreme summers likely were caused by climate change.

Earlier study has found broad trends linking earlier spring weather, rising temperatures and increased forest fires, suggesting that climate change may play a role in fires like the Waldo Canyon blaze outside of Colorado Springs, which has burned more than 18,000 acres and consumed about 300 homes.

The three tangibles seen that could cause collapse of the ecosystem as early as this century include climate change, population growth and environmental destruction, scientists warned in the journal Nature.